Detecting cancer early is critical to successful treatment. Within the last decade, a number of minimally invasive techniques for identifying pre-malignant tissue have been developed to address this issue. One of the most promising is elastic scattering spectroscopy (ESS), an "optical biopsy" technique that has demonstrated the capability of detecting abnormal lesions in a variety of organ systems. To date, this technique has been used in-vivo only with a pointdetection probe. In this proposal, a second-generation device for performing imaging elastic scattering spectroscopy 0ESS) is presented. The goal of this Phase I proposal is to fabricate a clinically-ready lESS system, and demonstrate that it can reliably quantitate scatterer size in tissue phantoms. Phase II will concentrate on clinical translational studies of this system, and will begin with a study of its use for detection of dysplasia in Barrett's esophagus. As part of the present proposal, an approved protocol for this initial trial will be developed.